A fuel cell power generating system is a system configured to generate electric power such that a hydrogen-containing gas and an oxygen-containing gas are supplied to a fuel cell stack (hereinafter referred to as “fuel cell”) that is a main body of a power generating portion, and a chemical energy generated by an electrochemical reaction between hydrogen and oxygen is utilized as an electric energy. Moreover, the fuel cell power generating system can generate the electric power with high efficiency and easily extract heat energy generated in an electric power generating operation to utilize the heat energy. Therefore, the fuel cell power generating system has been developed as a distributed power generating system capable of realizing high energy use efficiency.
Generally, the hydrogen-containing gas is not supplied from any infrastructure. Therefore, a conventional fuel cell power generating system is provided with a hydrogen generator including a reformer portion configured to generate the hydrogen-containing gas by causing a reforming reaction between steam and a raw material at 600° C. to 700° C. using a Ru catalyst or a Ni catalyst. Here, city gas, LPG, or the like supplied form an existing infrastructure is used as the raw material.
Usually, the hydrogen-containing gas obtained by the reforming reaction contains carbon monoxide derived from the raw material. If the carbon monoxide concentration of the hydrogen-containing gas is high, an electric power generation property of the fuel cell deteriorates. Therefore, in addition to the reformer portion, the hydrogen generator often includes reaction portions, such as a shift converter portion configured to cause a shift reaction between the carbon monoxide and the steam at 200° C. to 350° C. to reduce the carbon monoxide and having a Cu—Zn based catalyst or a precious metal based catalyst, and a selective oxidation portion configured to selectively cause an oxidation reaction of the carbon monoxide at 100° C. to 200° C. to further reduce the carbon monoxide and having a Ru catalyst or a Pt catalyst.
Catalytic activities of the catalysts, such as the Cu—Zn based catalyst, used by the above reaction portions may deteriorate by oxidation. For example, after the hydrogen generator stops operating, the inside of the hydrogen generator may become a reduced pressure state by the temperature decrease and the condensation of the steam, and outside air may be suctioned into the hydrogen generator, so that the catalyst may be exposed to an oxidation atmosphere. To suppress this phenomenon, it is desirable that when stopping the hydrogen generator, an inactive gas, such as nitrogen, be supplied to the hydrogen generator to realize an inactive gas atmosphere. However, as with the hydrogen-containing gas, the inactive gas is not supplied from any infrastructure. Especially, the inactive gas cannot be easily utilized in the distributed power generating system.
Here, to prevent the catalyst from being exposed to the oxidation atmosphere without using the inactive gas, for example, proposed is a configuration in which when stopping the hydrogen generator, an exit valve of the shift converter portion is closed to stop supplying the raw material and water to the reformer portion, and when the reformer portion and the shift converter portion become a predetermined temperature or lower, the exit valve of the shift converter portion open to supply the raw material to the hydrogen generator (see Patent Document 1 for example).
Moreover, proposed is a configuration in which when stopping the hydrogen generator, an output of at least one of a material supplying portion, a water supplying portion, and a combustion air supplying portion is controlled to lower a detected temperature of a reforming temperature measuring portion while continuously supplying the raw material and the water, and in a case where the detected temperature of the reforming temperature measuring portion falls below a predetermined reference temperature, the supply of the raw material and the supply of the water are stopped (see Patent Document 2 for example).
Patent Document 1: Japanese Laid-Open Patent Application Publication 2004-307236
Patent Document 2: Japanese Laid-Open Patent Application Publication 2006-8458